The purpose of this project is to better understand how drugs affect the mechanisms of the ionic conductance in membranes which are voltage-dependent and excitable. These studies involve the use of the squid giant axon and the nerve bundles from the garfish. We have continued studies on the mechanism of drug-channel interactions in the squid axon membrane. In particular, we have studied yohimbine and its analogs. In addition, we have studied amiodarone, an antiarrhythmic drug. We have shown that amiodarone has an acute effect on the electrical properties of the squid giant axon. This is one of the very few acute effects observed for amiodarone.